Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.94	7.809%	$89.4168	$89.42	$89.40	$89.40
Purchase #2	$239.65	9.524%	$262.4743	$262.47	$262.45	$262.50
Purchase #3	$83.71	10.485%	$92.487	$92.49	$92.50	$92.50
Purchase #4	$44.29	5.760%	$46.8411	$46.84	$46.85	$46.80
Purchase #5	$157.50	7.421%	$169.1881	$169.19	$169.20	$169.20
Purchase #6	$72.78	7.657%	$78.3528	$78.35	$78.35	$78.40
Purchase #7	$40.32	10.485%	$44.5476	$44.55	$44.55	$44.50
7 purchase totals =	$721.19		$783.3077	$783.31	$783.30	$783.30